Automatic power transmission control system

ABSTRACT

An automatic power transmission control system for a vehicle driven by an engine having a carburetor throttle valve which control system comprises a shift control unit to cause shifting of different gear reduction ratios in accordance with a signal representative of an effective opening area of the throttle valve and a signal representative of a vehicle speed, and a shift pattern generator circuit associated with the shift control unit and responsive to a signal representing a closed condition of the throttle valve for modifying the shift pattern whereby a downshift is effected from a lower gear reduction ratio to a higher gear reduction ratio regardless of the vehicle speed to provide sufficient engine braking action when the closed condition of the throttle valve is sensed.

I Umted States Patent 1191 1111 3,776,048

Enomoto et a1. Dec. 4, 1973 AUTOMATIC POWER TRANSMISSION 3,673,892 71972 Kato et a]. 74/866 x CONTROL SYSTEM 3,680,411 8/ 1972 Ito et a1.74/866 [75] Inventors: Koji Enomoto; Takayuki Akaishi; Primary Examinercharles l Myhre wataru an of Yokohama Assistant Examiner-Thomas C. PerryJapan Att0rney-Donal E. McCarthy et al. [73] Assignee: Nissan MotorCompany, Limited,

Yokohama, Japan ABSTRACT An automatic power transmission control systemfor a {-22} Flled' Sept 1971 vehicle driven by an engine having acarburetor throt- [21] Appl. No.: 177,603 tle valve which control systemcomprises a shift control unit to cause shifting of different gearreduction [30] Forelgn Apphcatlon Pnonty Data ratios in accordance witha signal representative of an Feb. 8, 1971 Japan ..46/4730 effectiveopening area of the throttle valve and a sig- [52] US. Cl. 74/866 nalrepresentative of a vehicle speed, and a hift [51] Int. Cl B601: 21/02tern generator circuit associated with the shift control [58] Field ofSearch 74/866, 877 unit and responsive to a signal representing a closedcondition of the throttle valve for modifying the shift [56] ReferencesCited pattern whereby a downshift is effected from a lower UNITED STATESPATENTS gear reduction ratio to a higher gear reduction ratio 2,399,5674 1946 Peterson eta] 74/866 x regifrdless the speed to Pmvide f f2,557,791 6/1951 Long 74/877 x engme b'akmg 9 when the c105 of 2,620,66712 1952 Flinn 74/877 x the throttle valve IS sensed 2,909,077 10/1959Kamins 74/866 3,088,337 5/1963 Bemmann... 74/866 X 3 Chums l1 DrawmgFlgures 3,646,835 3/1972 Ito et a]. 74/866 X a L l i 205 207 ,209 211212 1 215 1050 TSSSTTLE I 1st NhODl- T 1 2 R pg L 1 s1 2nd NING 1 SENSOR1 CIRCUIT COMPARATOR AMPUF'ER 1 SOLENO'D 20! 1 204 2061 2070 2103 2|?) 2I4 216 1040 VEHICLE ii: 2nd MOD! EOSO 2-5 REDUC- L 2 nd i 1st SPEED IFYING TlON RATIO AMPUFIER SOLENOID SENSOR C l RCU IT COMPARATOR I ZZI 1-CLOSED SHIFT THROTTLE PATTERN svvncn GENERATOR 1 219 g 5 FRICTION 218PATENIEDUEC 41915 3776348 sum 2 or 6 l FIRsT SHIFT Q5} H '9 VALVE iQZ -TOTTLE v VE LINE PRESSURE I I I26 REGULATOR VALVE 9 III 159 EMERGENCY I03I22 VALVE PATENTEU DEC 4 I915 SHEET U 0F 6 VEHICLE SPEED ozimmo 5Com;

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VEHICLE SPEED SPEED SIGNAL :1 AUTOMATIC POWER TRANSMISSION CONTROLSYSTEM This invention relates to an automatic power transmissionproviding a plurality of gear reduction ratios and, more particularly,to a control system of such power transmission. 1

An automatic power transmission of the planetary gear set type used in amotor vehicle commonly includes a control system for controlling theactuation of friction elements, such as friction clutches and brakes,which are selectively engaged and disengaged in sequence toautomatically effect successive shifts from one driving speed range gearreduction ratio to another. The shift patterns for such automatic shiftsare so arranged that the shift will automatically take place when theoutput shaft speed of the transmission exceeds a certain value. Aproblem is encountered with such shift patterns in that it is impossibleto automatically effect engine braking action when driving on verywinding roads, or, for example, turning sharply such as on mountainousand meandering roads. Thus, it is frequently necessary to applyundesirably a service brake or to manually cause the transmission toshift to its low speed lock-up position when going downhill or drivingon meandering roads with a result that it is difficult to attain thebasic purpose of automatic control, that is, to reduce driver's effortin vehicle operation.

It is, therefore, an object of this invention to provide an improvedcontrol system for an automatic power transmission providing a pluralityof gear reduction ratios.

Another object of this invention is to provide a control system adaptedfor automatically effecting an engine braking action when going downhillor when driving on winding roads.

Another object of this invention is to provide a control system adaptedfor automatically effecting downshift from the higher speed range gearreduction ratio to the lower speed range gear reduction ratio, that is,from a low input-output ratio to a high input-output ratio, thereby toprovide sufficient engine braking action when going downhill.

Another object of this invention is to provide a control system foreffecting downshift when closing an engine carburetor throttle valvewhile driving at a moderate vehicle speed.

In order to achieve these and other objects, the present inventioncontemplates to provide an additional switching means and an associatedcircuitry in an electronic control circuit forming a part of a knowncontrol system. This switching means is made responsive to a closedcondition of a carburetor throttle valve of the engine when goingdownhill or when driving on winding roads to generate an electricsignal. The electric signal thus generated is utilized for changing ashiftingsignal generated by the electronic control circuit wherebydownshift will be automatically effected from a low gear reduction ratioto a high gear reduction ratio to provide sufficient engine brakingaction when going downhill.

In the drawings:

FIG. I is a schematic diagram of an automatic power transmission towhich the control system according to this invention is applied;

FIG. 2 is a schematic diagram of a hydraulic control circuit forming apart of the control system according to this invention;

FIG. 3 is a block diagram illustrating an electronic control circuitforming a part of the control system according to this invention;

FIG. 4 is an example of conventional shift patterns;

FIG. 5 is an example of shift patterns which are attained in accordancewith the present invention;

FIG. 6 is a diagram of an electric circuitry causing downshifting totake place when an engine carburetor throttle valve is closed whiledriving at a moderate vehicle speed;

FIG. 7 is another example of shift patterns which are attained inaccordance with this invention;

FIG. 8 is a diagram illustrating a modified form of the electriccircuitry shown in FIG. 6; and

FIGS. 9 through 11 are views illustrating an example of the closedthrottle switch shown in FIGS. 3, 6 and 8.

The control system of the present invention will be. herein shown anddescribed as applied to an automatic power transmission providing threeforward drive gear reduction ratios and a reverse drive gear reductionratio and having a hydrodynamic torque converter by way of example only.It should, however, be understood that the control system of thisinvention is also applicable to a great veriety of automatic powertransmissions providing two or more than three forward drive gearreduction ratios. It should be understood that expressions such aupward, leftward, downward etc. used in the following description of thedrawings may or may not refer to such directional movements, actions orpositions in actuality and are applicable to the drawings only.

Referring now to FIG. 1, the automatic power transmission to which thisinvention is applied comprises a drive shaft 10 and a driven shaft 11.The drive shaft 1 is connected to a suitable prime mover such as aninternal combustion engine E, and the driven shaft 11 is connected todriving wheels (not shown) of the motor vehicle. The transmission hereinshown also comprises a turbine shaft 12 and an intermediate shaft 13which are in line with the shafts l0 and 11. The transmission alsocomprises a hydrodynamic torque converter 14 with a oneway brake l5,first and second hydraulically operated friction clutches 16 and 17,first and second hydraulically operated friction brakes 18 and 19, firstand second planetary gear sets 20 and 21, and a oneway brake 22.

The hydrodynamic torque converter 14 comprises, as customary, a bladedimpeller or pump 140, a bladed rotor or turbine 14b, and a bladedreaction element or stator 14c, The impeller 14a is driven from thedrive shaft 10, and the rotor 14b is fixed to the turbine shaft 12. Thestator 14c is rotatably mounted on a mechanism comprising a hollow shaft23 and the one-way brake 15 which is disposed between the stator 14c andthe hollow shaft 23.

The one-way brake 15 may be of any suitable con.- struction and is soarranged as to allow a free rotation of the stator 14c only in theforward direction of the vehicle, that is, in the direction in which thedrive shaft 10 rotates but not in the reverse direction.

The torque converter 14 operates in a manner well known for driving theturbine 14b at a greater torque than engine torque impressed on theimpeller 14a of the converter. The stator 14c functions to change thedirection of flow of the fluid from the turbine 14b to the impeller 14ain a positive direction so as to transfer this increased torque to theturbine 14b. The stator 14c tends to rotate in the same direction as thedirection in which the turbine 14b and the impeller 14a rotate whencertain speeds are reached by the last two elements, whereupon thetorque converter 14 now operates essentially as a fluid coupling inwhich the turbine 14b is driven at a substantially constant speed at agiven engine speed and without increase in torque with respect to theimpeller 14a.

The first planetary gear set has rotary members including an internallytoothed outer ring gear 24 which is connected to the intermediate shaft13, two or more planet pinions 25 which externally mesh with the outerring gear 24, and a sun gear 26 externally meshing with the planetpinions 25. The planet pinions 25 are carried by a pinion carrier 27which is connected with the driven shaft 11.

The second planetary gear set 21, similarly, has rotary membersincluding an internally toothed outer ring gear 28, two or more planentpinions 29 externally meshing with the ring gear 28, and a sun gear 30externally meshing with the planet pinions 29. The planetpinions 29 arecarried by a pinion carrier 31, which is shown as connected with a rotorof the one-way brake 22.

The rotary members (except the pinions) thus arranged are rotatableconcentrically about a common axis which is in line with the drivenshaft 11 connected to the pinion carrier 27 of the first planetary gearset 20. As illustrated by way of example, the sun gears 26 and 30 of thefirst and second planetary gear sets 20 and 21, respectively, areintegrally mounted on a hollow shaft 32 which is rotatable about thedriven shaft 11.

The first friction clutch 16 or front clutch may be of any suitableconstruction and in the illustrated preferred embodiment comprises adrive portion 33 connected to the turbine shaft 12, and a driven portion34 connected to a brake drum 35 which is integral with the hollow shaft32. The clutch 16 is actuated byan actuator (not shown), which will bediscussed hereinafter, for effecting engagement and disengagement of thedrive portion 33 to and from the driven portion 34 when a hydraulicpressure is applied and relieved, respectively.

The second friction clutch 17 or rear clutch similarly comprises a driveportion 36 connected to the turbine shaft 12 and a driven portion 37connected to the intermediate shaft 13. The rear clutch 17 is actuatedby an actuator (not shown) for engaging and disengaging the driveportion 36 to and from the driven portion 37.

The first friction brake 18 or band brake is shown to comprise a brakeband 38 adapted to act on the brake drum 35. The first brake 18 isactuated by an actuator (not shown) associated therewith for actuatingand releasing the same to brake or release the sun gears 26 and 30through the hollow shaft 32 connected thereto.

The second friction brake 19 or low and reverse brake comprises a rotorportion 39 which is connected to the pinion carrier 31 associated withthe one-way brake 22, and a stator portion 40 connected to atransmission housing 41. The low and reverse brake 19 is actuated by anactuator (not shown).

The one-way brake 22 may be constructed in any suitable fashion to allowa free rotation of the pinion carrier 31, connected with the rotor 39 ofthe low and reverse brake 19, only in the direction shown by arrow A.The power transmission thus constructed operates in a manner well knownto provide three automatically selected forward drive gear ratios, atsingle manually se lected forward drive gear reduction ratio and asingle reverse drive gear reduction ratio, through selective coupling ofthe clutches and brakes.

The operating conditions of the clutches and brakes for the differentdrives and the respective gear rations are tubulated in Table I, whereinthe sign denotes that the related clutch or brake is actuated and thesign denotes that the clutch or brake is kept released.

As seen in Table l, first speed range gear ratio in the automatic driveis established by engaging the second clutch 17 and the one-way brake22. With the one-way brake 22 actuated, the drive connection isinterrupted between the engine and the driving wheels of the motorvehicle when the power flow is reversed because of the overrunningnature of brake 22 so that engine braking does not take place. Thesecond speed range gear ratio is established when the first brake 18 isapplied with the second clutch 17 kept engaged. When the first brake 18is applied with the second clutch 17 kept engaged. When the first brake18 is applied, the drive connection maintained between the engine andthe driving wheels of the vehicle even when the power flow is reversedso that engine braking action is brought about. The third speed rangegear ratio is established by engaging the first clutch 16 with thesecond clutch 17 kept engaged. When the first clutch 16 is engaged, theengine braking action is brought about in the same manner as in thesecond speed range gear ratio. The first range gear ratio in the Lposition is established by engaging the second clutch l7 and the secondbrake 19. With the second brake 19 actuated, the drive connection ismaintained between the engine and the driving wheels of the motorvehicle even when the power flow is reversed so that engine braking isbrought about. The reverse drive is completed by engaging the firstclutch l6 and the second brake l9. When'the second brake 19 is actuated,engine braking action is brought about in the manner discussed above.

Referring to FIG. 2, a hydraulic control circuit is shown which controlsthe actuation of the friction elements thereby to selectively effectshafts of the different speed range gear ratios. The hydraulic controlcircuit is shown to include a fluid pump 100, a line pressure regulatorvalve 101, a throttle valve 102, a manual selector valve 103, a firstshift valve 104, a second shift valve 105 and an emergency valve 106.

The fluid pump 100 and a sump 107 serve as a source for supplying fluidunder pressure to the actuators of the friction elements, the torqueconverter and parts of the transmission to be lubricated. The fluid pump100 is adapted to be driven from the drive shaft through the bladedimpeller 14a of the torque converter 14. During the operation of theengine E, the fluid pump 100 functions to suck up fluid from the fluidsump 107 and deliver it to a conduit 108. The fluid pressure in thisconduit 108 is herein referred to as a line pressure. The line pressurein the conduit 108 is adjusted to a desired level by means of the linepressure regulator valve 101 for effecting smooth engagement of thefriction elements.

The line pressure regulator valve 101 comprises a valve spool 109 and aspring 110. The valve spool 109 is urged by the force of the spring 10upward. Another valve spool 111 is co-acting with the valve spool 109for thereby regulating the line pressure. The throttle pressure in aconduit 112 and the line pressure in a conduit 126 act through the valvespool 111 on the valve spool 109 and act against the pressure applied onthe upper part of the valve spool 109 from the conduit 108 through anorifice 114.

The pressurized fluid for operating the hydrodynamic torque converter 14is fed from the conduit 108 through the line pressure regulator valve101 to a conduit 115 and maintained at a proper level by the aid ofrelief valves 116 and 117. The fluid fed through the relief valve 117 isthen delivered through a fluid cooling device, not shown, to thecomponent parts of the power transmission to be lubricated. The throttlevalve 102 comprises a valve spool 118 and is connected through a plunger119 to a vacuum diaphragm (not shown) in a diaphragm housing 120 whichis connected through a conduit 121 to an intake manifold (not shown) ofthe engine. The inlet of the throttle valve 102 communicates with themain conduit 108 to cause the modulated throttle pressure to bedelivered to the regulator valve 101. The modulated throttle pressure isutilized for regulating'the line pressure in the main conduit 108 to anoptimum level for effecting smooth engagement of the friction elements.The fluid under pressure thus regulated is passed through the mainconduit 108 to the manual selector valve 103.

The manual selector valve 103 is shown to have the following positions:an R or reverse drive position, an N" or neutral position, a D orautomatically controlled forward drive position, and an L or manuallycontrolled forward low speed drive position. The man ual selector valve103 comprises a valve spool 122 which at each selected position servesto deliver the pressurized fluid introduced from the main conduit 108into any required conduit of conduits 123, 124, 125 and 126. Thepressurized fluid in the conduit 108 is delivered to the conduits 123,124, 125 and 126 in response to a selected position of the valve spool122 as shown in the following Table II. 1

TABLE II Conduit Conduit Conduit 123 124 125 126 R position N position Dposition L position In Table II, the sign means that the fluid underline pressure is introduced into the respective conduits at eachselected position and the sign means that the pressurized fluid isprevented from being delivered to the respective conduits.

The first and second shift valves 104 and 105 cooperate with each otherfor controlling the fluid flow to the friction elements thereby toeffect a shift of the different speed range gear reduction ratios.

The first shift valve 104 comprises a valve spool 127 and a spring 128.The spring 128 urges the valve spool 127 upward. The inlet of the shiftvalve 104 communicates with the conduit 124 leading from the manualselector valve 103 and-the outlet with a conduit 129 leading to theemergency valve 106. The valve spool 127 is subjected at its upper partto the pressure applied thereon for acting against the force of thespring 128.

On the upper end of the valve spool 127 a plunger 130 of a firstsolenoid 104a is mounted. The first solenoid 104a, which may be of anysuitable construction, controls the movement of the valve spool 127which in turn controls the flow of pressurized fluid through valve 104.

The second shift valve comprises a valve spool 131 and a spring 132. Thespring 132 urges the valve spool 131 upward. The inlet of the shiftvalve 105 communicates with the conduit 123 and the outlets withconduits 133 and 134. The conduit 133 communicates with the emergencyvalve 106 while the conduit 134 communicates with the actuator 18a ofthe first brake 18. The shift valve 105 communicates also with theconduit 126, with which the conduit 133 may communicate. On the upperend of the valve spool 131 a plunger 135 of a second solenoid 105a ismounted. The second solenoid 105a, which may be of any known suitableconstruction, controls the sliding of the spool 131 which in turncontrols theflow of pressurized fluid through valve 105.

The emergency valve 106 comprises a valve spool 136 and a spring 137 andcommunicates at its upper part with the conduit leading from the manualselector valve 103. The emergency valve 106 also communicates with theconduit 129, with which a conduit 138 may communicate. The conduit 138communicates with the actuator 16a of the first clutch 16 and therelease side of the actuator 18a of the first brake 18. The conduit 138may also communicates with the conduit 126'. The emergency valve 106further communicates with the conduit 133, with which a conduit 139 alsomay communicates. The conduit 139 communicates with the actuator 19a ofthe second brake 19.

The solenoids 104a and 105a for the first and second shift valves 104and 105 respectively, are operated by which the solenoid is energizedand a sign denotes a condition in which the solenoid is de-energized.

TABLE 111 Selected Position Speed Range 1st Solenoid 2nd Solenoid RReverse N 1st D 2nd 1st L 2nd When the manual selector valve 103 ismoved to the R position, the conduits 125 and 126 communicate with themain conduit 108 as seen from Table I1. Pressurized fluid from the mainconduit 108 is delivered through the conduit 125 to the upper part ofthe emergency valve 106, so that the valve spool 136 is moved downwardthereby establishing communications between the conduits 126 and 138 andbetween the conduits 133 and 139. The pressurized fluid delivered to theconduit 126 is then passed through the conduit 138 over to the actuator16a of the first clutch 16 and to the release side of the actuator 18aof the first brake 18.

' The pressurized fluid in the conduit 126 is also delivered to thesecond shift valve 105. Since, in this condition, the second solenoid ais de-energized as shown in Table III, .the valve spool 131 of thesecond shift valve 105 is moved upward by the action of the spring 132thereby establishing communication between the conduits 126 and 133.Consequently, the pressurized fluid in the conduit 126 is passed throughthe conduits 133 and 139 over to the actuator 19a of the second brake19. Thus, the first clutch l6 and the second brake 19 are engaged sothat the reverse drive ratio is established.

When the manual selector valve spool 122 is moved to the N position, theconduits 123, 124, 125 and 126 do not communicate with the main conduit108 as seen from Table II. In this condition no friction elements areengaged so that a neutral condition established.

When the manual selector valve spool 122 is moved to the D position, themain conduit 108 communicates with the conduits 123 and 124 therebyadmitting pressurized fluid thereto. The pressurizied fluid admitted tothe conduit 123 is passed directly to the actuator 17a of the secondclutch 17, which is consequently engaged at all times for all forwardspeed ranges. Pressurized fluid in the conduit 123 is also delivered tothe upper parts of the first and second shift valves 104 and 105. Thepressurized fluid admitted to the conduit 124 is further delivered tothe first shift valve 104 at an intermediate portion of valve 104.

Since the electronic control circuit operates to energize andde-energize the first and second solenoids 104a and 105a, respectively,in a manner prescribed in Table Ill, the forward driving speed rangegear ratios are effected by electric signals delivered to the solenoids104a and 105a.

When the selector valve is in D position and the first speed rangeelectric signal is generated by the electronic control circuit, both thefirst and second solenoids 104a and 105a are energized so that theplungers 130 and 135 are caused to protrude. Consequently, the valvespools 127 and 131 are moved downward against the forces of the springs128 and 132, respectively. In this condition, the communication betweenthe conduits 124 and 129 is interrupted, while communication between theconduits 123 and 133 is established. The pressurized fluid admitted tothe conduit 132 is accordingly delivered through the conduit 133 to theemergency valve 106. Since, in this condition, the valve spool 136 ofthe emergency valve 106 is moved upward by the force of the spring 137,the conduit 133 is closed by a land (not identified) of the valve spool136 so that fluid in the conduit 139 is not pressurized. Thus, only thesecond clutch 17 is engaged and, therefore, the first speed range gearreduction ratio is obtained by the acti gi of the one-way brake 22.

As the vehicle speed increases to the shifting point from the firstspeed range gear ratio to the second speed range gear ratio, then thesecond solenoid 1054 is de-energized with the first solenoid 104a keptenergized as seen from Table III, so that the valve spool 131 of thesecond shift valve 105 is moved upward by the force of the spring 132.Consequently, the conduit 123 communicates with the conduit 134, therebyadmitting pressurized fluid to the apply side of the actuator 18a of thefirst brake 18. Since, in this condition, the pressure in the releaseside of the actuator 18a is released through an exhaust port (notidentified) of the first shift valve 104 through the conduit 138,emergency valve 106, and conduit 129, the first brake 18 is engaged andthus the second speed range gear ratio is established, with the secondclutch being directly engaged by the selector valve 103, and the one-waybrake 22 being released. In this gear ratio engine braking action isefiected when the power flow is reversed.

As the vehicle speed further increases, both solenoids 104a and 105a arede-energized, so that the valve spools 127 and 131 of the first andsecond shift valves are moved upward by the forces of the springs 128and 132. The conduit 124 communicates with the conduit 129 therebypassing the pressurized fluid thereinto. Since the valve spool 136 ofthe emergency valve 106 is moved upward by the force of the spring 137,the conduit 129 communicates with the conduit 138 thereby pressurizingit. Pressurized fluid in the conduit 128 is delivered to the releaseside of the actuator 18a of the first brake 18 to cause the same to bedisengaged. Pressurized fluid in the conduit 138 is also delivered tothe actuator 16a of the first clutch 16. Thus, the first clutch 16 isengaged and the third speed gear ratio is obtained, the second clutchbeing already engaged.

When the manual selector valve spool 122 is moved to the L position, themain conduit 108 communicates with the conduits 123 and 125 therebyadmitting pressurized fluid theretofIhe pressurized fluid admitted tothe conduit 123 is delivered to the actuator 17a of the second clutch 17to cause the same to be engaged, while the presurized fluid admitted tothe conduit 125 is passed to the upper part of the emergency valve 106to cause the valve spool 136 to move downward against the force of thespring 137. When, in this condition, the second speed range electricsignal is generated by the electronic control circuit according to thisinvention, both the first solenoid 104a and the second solenoid 105a arede-energized so that the valve spools 127 and 131 are moved upward bythe forces of the springs 128 and 132, respectively. In this condition,the conduit 123 communicates with the conduit 134 thereby admittingpressurized fluid to the apply side of the actuator 18a of the firstbrake 18. Thus, the second speed range gear ratio is obtained byengagement of clutch 17 and brake 18.

When, however, the first speed range electric signal is generated by theelectronic control circuit, the second solenoid 1054 is energized withthe first solenoid 104a kept de-energized, so that the valve spool 131is moved to a position in which the conduit 123 communicates with theconduit 133. Since the valve spool 136 v of the emergency valve 106 ismoved downwardly by the pressure in line 125 acting on the upper part ofthe valve spool 136 against the force of the spring 137, the conduit 133communicates with the conduit 139. Consequently, the pressurized fluidadmitted to the conduit 133 is delivered through the conduit 139 to theactuator 19a of the second brake 19. The second brake 19 is thus engagedand the second clutch 17 is already engaged directly by the selectorvalve 103, so that the first speed range gear ratio is established toeffect engine braking action in the vent that the power flow isreversed.

The electronic control circuit as described hereinabove is schematicallyillustrated in block form in FIG. 3. As shown, the electronic controlcircuit comprises a throttle opening sensor 200, a vehicle speed sensor201 and a shift control unit 202.

The throttle opening sensor 200 detects an effective open area of athrottle valve of a carburetor (not shown) of the engine E and isadapted to generate a voltage signal corresponding to the detectedvalue. The vehicle speed sensor 201 detects the speed of the drivenshaft 11 and is adapted to generate a voltage signal corresponding tothe detected speed. The generated voltage signals are then deliveredthrough lines 203 and 204 to first and second modifying circuits 205 and206, respectively, where each of these voltage signals is modified intorespective suitable forms for subsequent use. The voltage signals thusmodified are then fed through lines 207 and 208 to a 1-2 gear reductionratio comparator circuit 209 and a 2-3 gear reduction ratio comparatorcircuit 210, respectively. A line 207a connects line 207 to comparatorcircuit 210, and a line 208a connects line 208 to comparator circuit209. These gear reduction ratio comparator circuits 209 and 210 comparethe two voltage signals delivered from the first and second modifyingcircuits 205 and 206 thereby to generate control signals, respectively,for effecting a required shift of the different driving speed range gearreduction ratios. The control signal delivered from the 1-2 gearreduction ratio comparator circuit 209 is supplied through a line 211 toa first amplifier 212 while the control signal delivered from the 2-3speed ratio comparator circuit 210 is fed through a line 213 to a secondamplifier 214. The first and second amplifiers 212 and 214 amplify thecontrol signals delivered from the gear reduction ratio comparatorcircuits 209 and 210 and supply the amplified control signals throughlines 215 and 216 to the second and first solenoids 105a and 104a,respectively, for actuating them. These first and second solenoids 104aand 105a have two operating positions, which, as seen from Table III,are correlated with the operating positions of the associated shiftvalves of the hydraulic control circuit 217 to control the fluid flow tothe actuators of the friction elements 218 thereby to selectivelyprovide the three forward drive speed range gear reduction ratios andthe single reverse drive gear reduction ratio.

The primary purpose of the electronic control circuit is to serve as ashift pattern generator for causing operation of the first and secondsolenoids 104a and 105a to effect the shifts. FIG. 4 illustrates astandard shift pattern which has heretofore been proposed in the priorart. In FIG. 4, the curve p is formed of the shifting points at whichthe first speed range gear reduction ratio is shifted to the secondspeed range gear reduction ratio in dependence on throttle opening andvehicle speed and the curve q is formed of the shifting points at whichthe second speed range gear reduction ratio is shifted to the firstspeed range gear reduction ratio, while the curve r is formed of theshifting points at which the second speed range gear reduction ratio isshifted to the third speed range gear reduction ratio, and the curve sis formed of the shifting points at which the third speed range gearreduction ratio is shifted to the second speed range gear reductionratio. The points at which downshifts will automatically take place fallon line K when an accelerator pedal (not shown) is fully depressed. Itwill be seen, that since the transmission remains in the third speedrange gear even when the accelerator pedal is released to decrease theeffective throttle opening from a valve A to the closed position B whengoing downhill or during driving on very winding roads or for example,turning sharply such as on mountainous and meandering roads, it isimpossible to effect sufficient engine braking action. Thus, it isnecessary to apply undesirably the service foot brake or to effectdownshifting by manually moving the selector lever to the L position inorder to obtain engine braking action under emergency conditions.

In order to eliminate these drawbacks encountered in the prior art, thepresent invention proposes to control the pwer transmission in such amanner that the particular range is automatically selected within whichthe braking effect of the engine is best when going downhill or whendriving on winding roads. An example of the shift pattern to attain thispurpose is represented in FIG. 5, wherein like curves are designated bythe like letters as used in FIG. 4 except that a prime has been added tothose,,respectively. As seen from FIG. 5, the curves r and s' are variedto higher vehicle speed levels so that the shifts will take place athigher vehicle speed levels than seen in FIG. 4. However, if theaccelerator pedal is released to decrease the effective throttle openingfrom the point A, representing the third speed range gear ratio drivingcondition, to the point B, then the downshift will be automaticallyeffected from the third speed range gear ratio to the second speed rangegear reduction ratio thereby to effect sufficient engine braking actioneven though the vehicle speed V, is still considerably higher than thatat which downshifting would normally take place. It will be appreciatedthat although the shift pattern is shown as of the type to effect thedownshift merely from the third to the second speed range gear ratio-inFIG. 5, various modifications can be made so as to effect the downshiftfrom the second to the first speed range gear reduction ratio, ifdesired.

To automatically effect downshift from the higher vehicle speed gearreatio to the lower vehicle speed gear reduction ratio thereby. toprovide sufficient engine braking action when going downhill or whendriving on winding roads, the electronic control circuit furtherincludes a closed throttle switch 219 and a shift pattern generator 220,as shown in FIG. 3. The switch 219 senses and responds to a closedthrottle condition of the throttle valve of the engine E by closing anelectric circuit while driving and completelyreleasing an accelerationcontrol member. An electric signal is thus developed and fed through aline 221 to the shift pattern generator 220, to which the voltage signalindicative of the vehicle speed is also delivered through the line 208afrom the second modifying circuit 206. Upoin receiving these signals,the shift pattern generator 220 generates a shift pattern for producinga shifting signal which is transmitted through a line 222 to theamplifier 214. The shifting signal delivered to the amplifier 214 isthen delivered through the line 216 to the first solenoid 104a foractuating the same thereby to effect downshift from the third to thesecond speed range gear reduction ratio when the throttle valve issubstantially closed while driving.

Referring next to FIG. 6, there is schematically shown an example of theshift pattern generator 220 and the amplifier 214 associated therewithforming a part of the electronic control circuit according to thepresent invention. As shown, the shift pattern generator 220 includestwo transistors and a plurality of resistor elements. The firsttransistor, designated at 230, is connected at its base to a junction231 between a resistor 232 connected to a terminal 233 and an adjustableresistor 234 connected to a junction 235. The terminal 233 is connectedto the vehicle speed sensor 201 through the modifying circuit 206 (seeFIG. 3) and receives the voltage signal indicative of the vehicle speed.The junction 235 is connected to the closed throttle switch 219, whichin turn is connectable to a positive terminal 236 of a d.c. electricpower source (not shown). The collector of the transmistor 230 isconnected through a junction 237 to a resistor 238 connected to thejunction 235, and the emitter thereof is grounded. The secondtransistor, designated at 239, is connected at its base to a junction240 between resistors 241 and 242. The resistor 241 is connected to thejunction 237 while the resistor 242 is grounded. The collector of thetransistor 239 is connected to a junction 243 between resistors 244 and245, and the emitter thereof is grounded. The resistor 244 is connectedto the junction 235, while the resistor 245 is connected to the base ofa transistor 246 of the amplifier 214. The collector of the transistor246 is connected through a protecting diode 247 to a positive terminal248 of an electric power source (not shown), while the emitter of thetransistor 246 is connected to the base of a transistor 249. Thecollector of the transistor 249 is connected to the solenoid 104a, andthe emitter thereof is grounded.

If the accelerator pedal is released to close the throttle valve whenthe vehicle is running in the third speed range gear ratio, the closedthrottle switch 219 is closed so that the positive voltage is suppliedto the junction 235 from which the voltage is supplied through theadjustable resistor 234 to the base of the transistor 230. When thevehicle is running at a speed below a predetermined level, the negativevoltage indicative of the vehicle speed is so low that the voltagesupplied to the junction 231 goes positive thereby rendering thetransistor 230 conductive. With the transistor 230 energized, thevoltage supplied to the junction 240 goes zero so that the transistor239 is made non-conductive. Consequently, the voltage supplied from theterminal 236 connected to the electric power source (not shown) issupplied through the junction 243 to the base of the transistor 246 ofthe amplifier 214. Thus, the transistors 246 and 249 are made conductiveto energize the coil of the first solenoid 104a. It should be noted, inthis instance, that the hydraulic control cir cuit and accordingly thepower transmission are oper ated to automatically effect downshift fromthe third to the second speed range gear reduction ratio according tothe schedule set forth in Table III. When, however,

the vehicle is running at a speed above the predetermined level, thenthe negative voltage indicative of the vehicle speed increases so thatthe voltage appearing at the junction 231 goes negative therebyrendering the transistor 230 non-conductive. This causes the transistor239 to become conductive so that the voltage ap pearing at the junction243 will be zero whereby the first solenoid 1040 is de-energized. Itshould be kept in mind that it is possible to determine the shiftingpoint at which the downshift will take place by varying the value of theadjusting resistor 234.

Another example of the shift pattern is illustrated in FIG. 7, whereinnumerals 1, 2, 3 and 4 indicate the first, second, third and fourthspeed range gear reduction ratio shifting patterns, respectively. InFIG. 7, the respective speed levels at which downshifting takes placeare shown as extended to respective higher speed levels, V V and Vrespectively, whereby the downshift may take place from the fourth tothe third, from the third to the second and from the second to the firstspeed range gear reduction ratio so that engine braking may be effectedwhen required. FIG. 3),

FIG. 8 illustrates a modified form of the shift pattern generator 220which is combined with the 2-3 speed range gear ratio comparator circuit210. In this illustrated embodiment, the shift pattern generator 220'incorporates therein the closed throttle switch 219' which intervenesbetween a resistor 255 and a terminal 236' to which voltage is appliedfrom a suitable electric power source. The resistor 255 is connected toa junction 256 between resistors 257 and 258. The resistor 157 isconnected to the first modifying circuit 205 which in turn is connectedto the throttle opening sensor 200 (see FIG. 3), while the resistor 258is connected to the second modifying circuit 206 connected to thevehicle speed sensor 201. The voltage signal indicative of the throttleopening is supplied through the resistor 257 to the junction 256, towhich the voltage signal indicative of the vehicle speed is alsosupplied through the resistor 258. The junction 256 is connected tojunction 259, which in turn is connected to the base of transistor 260.The collector of the transistor 260 is connected to a junction 261 ofresistors 262 and 263 and the emitter thereof is grounded. The resistor262 is connected to a terminal 264, to which a voltage is supplied froma suitable electric power source. The. resistor 263 is connected to ajunction 265 which in turn is connected to the base of a transistor 266.The base of the transistor 266 is also grounded through a resistor 263'.The collector of the transistor 266 is connected to a junction 267 whichin turn is connected through a resistor 268 to the terminal 264. Thejunction 267 is connected through a resistor 268' to the junction 259and is also connected through a junction 269 to the first solenoid 104a.

When the accelerator pedal is depressed the closed throttle switch 219is opened so that no signal is supplied to the junction 256 from theterminal 236' of the power source. However, the throttle signal and thevehicle speed signal are supplied to the junction 256 from the throttleopening sensor 200 and the vehicle speed sensor 201, respectivelythrough the first and second modifying circuits 205 and 206,respectively. If, in this instance, the vehicle is running at a speedcorresponding to the second speed gear ratio, then the amplitude ofvehicle speed signal is lower than that of the throttle signal so thatthe voltage appearing at the junction 256 goes positive. Consequently,the transistor 260 is made conductive whereby the voltage appearing atthe junction 261 and accordingly the voltage appearing at the junction265 are zero. This causes the transistor 266 to become nonconductive andthus the voltage derived from the electric power source is suppliedthrough the resistor 268 to the first solenoid 104a maintaining the sameenergized whereby the transmission continues to be in the second speedrange gear ratio. In this condition, the resistor 268 functions toprovide a hysteresis in the shift pattern. The voltage signal appearingat the junction 269 is fed through the resistor 268 back to the junction256, whereby the downshift is effected in a normal manner, for example,as seen in FIG. 4.

When, however, the accelerator pedal is released when going downhill,then the closed throttle switch 219' is closed so that the closedthrottle signal is further supplied to the junction 256 whereby theshift pattern is changed for the shifting to take place at a highervehicle speed level. This is an important feature of the presentinvention. Since, in this instance, the hysteresis of the shift patternis adapted to depend on the value of the resistor 268, the samehysteresis will be obtained as in the event that no closed throttlesignal is supplied to the junction 256.

An example of the closed throttle switch is illustrated in FIGS. 9, land 1 1 wherein like component parts are designated by same numerals. Asshown in FIG. 9, the closed throttle switch 219 is actuated by anaccelerator pedal 270 associated with a connecting lever 271 foractuating a throttle valve 272. The closed throttle switch 219 has acasing 273 which is mounted on the upper portion of the acceleratorpedal 270. A reed switch 274 is secured to the inner wall of the casing273. A magnet 275 is disposed adjacent to the reed switch 274 forselectively energizing the same. The closed throttle switch 219 also hasa screen member 276 which is disposed between the reed switch 274 andthe magnet 275 and is pivotally supported by a pin 277.

A spring 278 is provided for urging the screen member 276 away from themagnet 275 thereby to cause the reed switch 274 to be closed by theaction of the magnet 275. The screen member 276 is actuated by theconnecting rod 271 controlled by the accelerator pedal 270.

When, in operation, the accelerator pedal 270 is depressed, theconnecting rod 271 and accordingly the screen member 276 is moved in aposition to effect screening action against the force of the magnet 275.Consequently, the reed switch 274 is opened. When, on the contrary, theaccelerator pedal 270 is released, then the screen member 276 is movedaway from the magnet 275 by the force of the spring 278. Accordingly,the reed switch 274 is magnetized by the action of the magnet 275 and,therefore, the reed switch 274 is closed.

From the foregoing, it will be seen that a control sys- 14 tem accordingto this invention allows the power transmission to automatically effectforced downshift from a lower gear reduction ratio to a higher gearreduction ratio when an engine carburetor throttle valve is closedwhereby engine braking action is successively effected.

What is claimed is:

1. An electronic control system for an automatic power transmission fora motor vehicle driven by an engine having a carburetor throttle valvecontrolled by an accelerator pedal comprising, in combination; gearratio changing means, first sensing means for generating first voltageproportional in magnitude to vehicle speed; second sensing means forgenerating second voltage of opposite polarity to the first voltage andproportional in magnitude to effective open area of said carburetorthrottle valve; circuit means connected with said gear ratio changingmeans for effecting the operation thereof including inputs connected tosaid first and second sensing means to receive said first and secondvoltages therefrom, and further including means for comparing the firstand second voltages and producing a first set of shifting signals tocause said gear ratio changing means to effect shift into different gearratios in accordance with a predetermined shift schedule in dependenceon said first and second voltages; and control means including aconstant voltage power supply means connected to said inputs of saidcircuit means to supply a third voltage of opposite polarity to saidfirst voltage thereto and switching means connected'between saidconstant voltage power supply means and said inputs of said circuitmeans, said switching means cooperating with said accelerator pedal fortransmitting said third voltage to said inputs of said circuit meanswhen said carburetor throttle valve is closed, and said comparing meansproducing a second set of shifting signals to cause said gear ratiochanging means to effect shift into different gear ratios in accordancewith another predetermined shift schedule in dependence on'said first,second and third voltages, whereby downshift will take place at a highervehicle speed level than normal when said throttle valve is closed.

2. An electronic control system according to claim 1, further comprisinga resistor connected between said switching means and said inputs ofsaid circuit means.

3. An electronic control system according to claim 1, in which saidswitching means includes a reed switch, a magnet for selectivelyenergizing said switch, a screen member, a spring urging said screenmember away from said magnet for de-energizing said switch, all of saidelements being disposed in a housing formed in said accelerator pedal, aconnecting rod linked with said throttle valve, and said connecting rodbeing arranged to act upon said screen member to open said reed switchin response to a depression of said accelerator pedal.

1. An electronic control system for an automatic power transmission fora motor vehicle driven by an engine having a carburetor throttle valvecontrolled by an accelerator pedal comprising, in combination; gearratio changing means, first sensing means for generating first voltageproportional in magnitude to vehicle speed; second sensing means forgenerating second voltage of opposite polarity to the first voltage andproportional in magnitude to effective open area of said carburetorthrottle valve; circuit means connected with said gear ratio changingmeans for effecting the operation thereof including inputs connected tosaid first and second sensing means to receive said first and secondvoltages therefrom, and further including means for comparing the firstand second voltages and producing a first set of shifting signals tocause said gear ratio changing means to effect shift into different gearratios in accordance with a predetermined shift schedule in dependenceon said first and second voltages; and control means including aconstant voltage power supply means connected to said inputs of saidcircuit means to supply a third voltage of opposite polarity to saidfirst voltage thereto and switching means connected between saidconstant voltage power supply means and said inputs of said circuitmeans, said switching means cooperating with said accelerator pedal fortransmitting said third voltage to said inputs of said circuit meanswhen said carburetor throttle valve is closed, and said comparing meansproducing a second set of shifting signals to cause said gear ratiochanging means to effect shift into different gear ratios in accordancewith another predetermined shift schedule in dependence on said first,second and third voltages, whereby downshift will take place at a highervehicle speed level than normal when said throttle valve is closed. 2.An electronic control system according to claim 1, further comprising aresistor connected between said switching means and said inputs of saidcircuit means.
 3. An electronic control system according to claim 1, inwhich said switching means includes a reed switch, a magnet forselectively energizing said switch, a screen member, a spring urgingsaid screen member away from said magnet for de-energizing said switch,all of said elements being disposed in a housing formed in saidaccelerator pedal, a connecting rod linked with said throttle valve, andsaid connecting rod being arranged to act upon said screen member toopen said reed switch in response to a depression of said acceleratorpedal.